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What happens to aerofoil downwash with Flaps extended vs retracted and how does it affect the Tail down force?
In my logic: Flaps extended will cause a greater Angle of Attack, to maintain Straight and Level Flight, AoA will be reduced, due to the increased "Surface", this allows to fly at lower Angle of Attack, tis means lower induced Drag causing downwash to decrease? However why does this result in an increased Tail Down Force and how does the downwash of the wing affect the tail force?

See last paragraph of my answer-- the nuance here is, we have to consider whether the question is about what happens to the tail downforce upon flap deployment if the tail configuration (including elevator position) remains exactly the same, or what has happened to the tail downforce after flap deployment after the aircraft has been re-trimmed to hold some given parameter constant (such as airspeed) -- or both.

A flap works increasing camber, angle of attack and surface of the airfoil.
Anyway, in order to compare the change of the aerodynamic characteristics in respect to the basis airfoil, everything is packed inside the relevant coefficients: if before deploying the flaps the wing has a NACA 65012 airfoil, an AoA of 2° and a surface of 100m², after the deployment of the flaps the wing still has a NACA 65012 airfoil, an AoA of 2° and a surface of 100m². Anyway $C_l$, $Cd$ and $C_m$ they all have changed and, in particular, they all have increased, as visible in the following pictures taken from this report:

Here we see the trends of $C_l$, $Cd$ and $C_m$ for several flap angles. The black line is the one for the basis airfoil. The plot for $C_l$ is shifted upward toward higher lift; the plot for $Cd$ is also shifted upward toward higher drag; and the plot for $C_m$ becomes more and more negative i.e. more and more pitch nose-down.

why does this result in an increased Tail Down Force?

In order to compensated for the:

lift increment $\rightarrow$ speed and AoA are decreased;
drag increment $\rightarrow$ thrust is increased, albeit the previous decrement in speed and AoA partially offset this;
higher nose-down pitch $\rightarrow$ tail downforce is increased.

Plus, flaps are deployed slowly and in steps.
Downwash is proportional to lift which, in turn, equals weight. Not changing the weight during the deployment of the flaps, downwash doesn't change too, at least globally: there's a local increase of lift (and therefore downwash) on the flapped surfaces of the wing and a local decrease on the non-flapped surfaces, but globally it remains the same.

how does the downwash of the wing affect the tail force?

If the higher downwash shed from the flapped surfaces impinges on the horizontal tailplane, its AoA has to be adjusted not only to compensate for the higher wing's $C_m$ but also for the changed local airflow. Note that these two effects are one the opposite of the other.

In the specific case of radio-controlled model gliders with the wings mounted at about the same level as the horizontal tail, I've found the following:

Deploying flaps that only cover the inboard portions of the wing, i.e. the portions of the wing in front of the horizontal tail, causes the aircraft to pitch up to a higher angle-of-attack.  If the aircraft was initially trimmed to fly near best-glide or min-sink speed, then after flaps are deployed, a nose-down stick (elevator) input may need to be maintained to prevent the aircraft from stalling, unless the aircraft is re-trimmed.

Deploying flaps that cover the entire wingspan causes the aircraft to pitch down to a lower angle-of-attack and gain airspeed, at least in cases where the wingspan is large compared to the span of the horizontal tail, unless a nose-up stick (elevator) input is maintained, or the aircraft is re-trimmed.

With a high-wing full-scale airplane such as a Cessna 152 or Cessna 172, lowering the flaps (which only cover the inboard portions of the wing) cause the aircraft to pitch up to a higher angle-of-attack and a lower airspeed, especially at high power settings.  If the aircraft was initially trimmed to fly near best-glide or min-sink speed, then after flaps are deployed, a nose-down stick (elevator) input may need to be maintained to prevent the aircraft from stalling, unless the aircraft is re-trimmed, especially at high power settings.  In this case, it's clear that the flaps are creating a stronger downwash over the horizontal tail, especially at high power settings, which more than offsets the increased nose-down pitching moment associated with increasing the camber of the wing.
So in all these cases we have a "balancing act"-- increasing the camber of the wing causes the wing to create a stronger nose-down pitching moment, but also increases the downwash over the tail, which creates a nose-up pitching moment.  The "balance" tends to be tipped toward the former factor if the span of the tail is small compared to the span of the portion of the wing covered by the flaps.  However a strong propwash tends to tip the balance toward the latter factor, if the flapped portion of the wing and the horizontal tail are both in the propwash.
If you are asking about the tail downforce after the aircraft is re-trimmed as needed to maintain the original airspeed, then you can be sure that the tail downforce is increased (or tail upforce is decreased) after the flaps are deployed, regardless of any other factors.  This is due to the way that the wing's pitching coefficient and pitching moment increase when the camber of the wing is increased.  But since the tail often lies in the downwash of the flapped portion of the wing, this simple observation alone isn't sufficient to tell us whether the elevator would have to be re-positioned higher, or lower, or neither, to deliver the appropriate increase in tail downforce (or decrease in tail upforce).

Not really a complete answer but still intended to convey some relevant useful info--


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Can a jet stream make a subsonic plane fly at a supersonic speed relative to the ground?
If a plane flies with a jet stream, its speed relative to the ground is the sum of the speed of the jet stream and the speed of the plane relative to the air in the jet stream. If the speeds that are added together are subsonic, can the resulting speed of the plane relative to the ground become supersonic? If it can, does the plane create a sonic boom on the ground?

Consider the converse case, a supersonic jet flying into a headwind. Would you expect the sonic boom to go away?

The speed of sound, supersonic flight, and the sonic boom are irrelevant to ground speed. The only thing that counts is the air speed and atmospheric conditions.

752 Knots  = 865 MPH = 1,393 KPH https://groundspeedrecords.com/wof-top-3/?aircraft-manufacturer=Boeing&wpvaircraftmodel=b747-400&term_id=432

"Supersonic speed relative to the ground" does not make sense. The speed of sound is always relative to the surrounding fluid (air). Air molecules do not care how the earth below is moving

Yes, the ground speed of a subsonic aircraft could be larger than the speed of sound. As an example, during the record time for a subsonic Atlantic crossing a Boeing 747 reached speeds of up to 1327 km/h:

Experts are hailing a British Airways flight as the fastest subsonic New York to London journey.
The Boeing 747-436 reached speeds of 825 mph (1,327 km/h) as it rode a jet stream accelerated by Storm Ciara.

(BBC)
The speed of sound at sea level is usually around 1235 km/h. The speed of sound is however temperature dependent and will be lower at high altitudes, therefore the ground speed in this case was higher than the speed of sound, regardless of the altitude.
This does not make the aircraft supersonic. A supersonic flight implies that the TAS (True AirSpeed) is higher than the local speed of sound. This was never the case for this 747 flight.

If it can, does the plane create a sonic boom on the ground?

No, a sonic boom can only be created locally by an aircraft flying faster than the local speed of sound. It is unrelated to the ground speed.
Consider the following illustration of a sonic boom:

(image source: Wikipedia)
You can see a line of sound waves currently hitting the person standing on the ground. This is the sonic boom you would hear.
I modified this image for subsonic flight:

You can see that the circles never intersect and can therefore never form a line of sound waves. If the aircraft is in a tailwind, the sound waves would be emitted in the same way, they would just move faster across the ground as a whole, but there is no relative difference between them (and the aircraft). Therefore, there is still no sonic boom even when the aircraft's ground speed is faster then the speed of sound.
Note however that the wind speed would change with altitude. The jet stream does not extend all the way to the ground. This would distort the circles when they get closer to the ground, but it cannot create a sonic boom.

"No, a sonic boom would be created locally" - Isn't that meant to read "NOT" ?

Is there any danger of the plane "falling out of" the jet stream, or encountering a patch of air which is moving slower which would (at the least) creating severe turbulence and at worst cause the plane to unintentionally go supersonic (at least for a brief time)?

If the plane deliberately made a sharp turn (or dive or climb) then it could exit the jetstream.

@Michael Not really. The edges of the jet stream are relatively sharp compared to normal changes in wind speeds. They are however not real discontinuities. There is still some smooth transition into slower wind speeds. Even if there would be a sharp change in wind speed or direction (called windshear), the doppler radar would pick it up and warn the pilots.

What happens when the sound waves from the plane overtake the sound waves emitted earlier, if the plane is moving faster than the sound waves due to a tailwind? Does it just sound like it's flying backwards, as you hear the noise moving away from you instead of closer?

@nick012000 That cannot happen. The sound waves are also travelling in the air, which is moving w.r.t. the ground, just like the plane. The whole picture of plane and emitted sound waves does not change with the wind.

@Bianfable What about when the plane is traveling through a layer of air that ends above the ground, though? Imagine a situation where the air from ground level to 10000 feet is stationary, and then at 10000 feet, a layer of air moving mach .4 starts, with a small laminar flow transition region between them. If a plane is flying at mach .8 at 20000 feet, then it would be moving at mach 1.2 relative to a person observing it on the ground, and it'll overtake the sound of its own motion once that sound leave the laminar flow zone and enters the stationary air, right?

@nick012000 Yes, the plane at 20,000 ft could overtake its own soundwaves at lower altitudes, but so what? It will not overtake the sound waves at 20,000 ft since they will move with the wind. It does not really matter that the sound waves below the aircraft are smoothly slowed down in the transition region. This cannot create a sonic boom.

@Bianfable I didn't say it would, but the person on the ground would hear it moving away from them because it overtakes its sound waves, right?

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How does downwash affect angle of attack?
Many aerodynamics textbooks, as well as many answers on here and similar websites claim that the downwash downstream of a wing induces a net angle of attack that is lower than just looking at flow direction and chord orientation would have you believe. They then often go on to say that lift is perpendicular to this "induced flow direction", explaining that the component parallel to the originally perceived flow direction is induced drag. I struggle with this idea, because my current understanding of lift dictates that downwash itself is a product of lift generation and therefore a product of angle of attack.
Also, when looking at visualisations of flow fields around a wing, we can see both upwash ahead of the wing and downwash behind it. Intuitively, I'm inclined to think that the downwash, being downstream of the wing, can't really affect the flow dynamics around the wing anymore. Conversely, the upwash, being upstream of the wing, should affect the flow around it, increasing angle of attack and therefore lift produced.

The only explanation I've come up with is this, though I'm not sure if it's correct:
Since any wing producing lift must introduce a net downwash on the surrounding air, the average air movement over the whole wing must also be negative. I guess my problem with this explanation is that I've always thought of angle of attack as a function of just chord orientation and flow direction. Is it correct to assume that, looking at the flow field closely around a wing, "traditional angle of attack" doesn't matter as much since the large induced flow velocities in front of the wing will make actual "aerodynamical" angle of attack, i.e. the angle at which the oncoming air actually hits the wing (as opposed to the angle between freestream flow direction and chordline) differ significantly?
I apologise if my question isn't very comprehensible, I had quite a hard time formulating it. In any case, I'd be glad for an answer, and I'll try my best to clarify what's unclear.

Is it correct to assume that, looking at the flow field closely around a wing, "traditional angle of attack" doesn't matter as much since the large induced flow velocities in front of the wing will make actual "aerodynamical" angle of attack, i.e. the angle at which the oncoming air actually hits the wing (as opposed to the angle between freestream flow direction and chordline) differ significantly?

Yes. Just witness the angle at which slats are pointing down: They are oriented to the local direction of flow which is strongly up at the leading edge when the coefficient of lift is high.

Typical landing configuration of an airliner wing, from an article by A. M. O. Smith, McDonnell-Douglas, in Journal of Aircraft, Vol 12 No 6, 1975. As always: Converging streamlines indicate accelerating flow and falling pressure while diverging streamlines show decelerating flow and rising pressure.
Note that the double slotted flap here is instrumental in inducing this steep local flow angle: Without it, the wing would not produce nearly as much lift and the suction on the upper side would be much weaker, causing less local bending of the direction of flow.
Note as well that the angle of attack of the airfoil is 0° while the streamlines entering the drawing on the left already have a marked upwash angle. The same happens in reverse at the right side where the flow shows a distinct downwash. This is a 2D simulation and at infinite distance to the airfoil the direction of flow is strictly horizontal. On both sides, because this airfoil does not produce induced drag in 2D flow (an effect also known as d'Alembert's paradox).
On a real wing, however, the tip effects reduce the lift curve slope so the local wing section will show a lower lift coefficient at the same geometrical angle of attack. Now suction and upwash are reduced (but still exist) and the air flowing off the wing leaves it with an added downward speed component. The far-field flow pattern now does not any more have the symmetry of equal up- and downwash. Instead, the downwash angle is increased to twice the magnitude of the reduced upwash angle because the influence of the free vortices in the wake must be added. The result is a backward tilt of the sum of all pressure forces acting on the wing which we call induced drag.

I'm struggling a bit with the last part of your answer. What exactly do you mean by "tip effects"? Also, if lift coefficient, and in turn suction and upwash are reduced, wouldn't the downwash be reduced too, since it is proportional to downwash angle/lift generated?

@MoritzHeppler "Tip effects" is the reduction of lift due to pressure equalisation at the wing tips. Yes, downwash would be reduced without the additional effect of the free vortices which are shed precisely because circulation goes to zero at the tip. So the tip effects increase the downwash behind the wing (more precise: In the inner $\pi/4$) and add an upwash left and right of it.

So the increase in downwash on a 3d wing compared to a 2d (or rather, the presence of a net downwash at all) occurs only due to the wake rolling up in itself? If that's the case, I have another question: the wake only starts rolling up when it has left the wing, so how can it still induce a downwards flow in the air still affecting a wing? Or is the point that the apparent downwash you'd see on a field of streamlines isn't entirely due to the pure lift produced by a wing, but rather a combination of it and the wake vortices further "blowing" the air aft of the wing downwards?

@MoritzHeppler No, wake rollup is only the consequence of lift and drag. The free vortices (which will form the wake) induce that downwash on the whole flow field around the wing, so it is tilted compared to the 2D case. I shouldn't have said "behind the wing" but "on and behind the wing".

I think I'm having some trouble with wording. Would it be correct to say that, because of the tip effects (i.e. pressure changing towards ambient/freestream pressure the closer you get to the tip) and following spanwise flow, the wake is made up of vortices, which is why it rolls up in itself?

@MoritzHeppler: That is exactly right. Most authors call the local flow around the wing tip the tip effect. But this is too narrow. When you include the gradual decrease of lift from the wing's middle towards the tips in that definition, it becomes correct.

How does that tie in to the benefits of a high aspect ratio? Say wing area is kept the same, but there is a span extension. Obviously you turn more air to a lesser extent rather than less air more strongly, so AoA and pressure differential between upper and lower surface is smaller, i.e. average pressure on both surfaces is closer to freestream pressure. Therefore, the pressure change along span is less pronounced, meaning less spanwise flow -> weaker wake vortices -> less downwash induced -> less induced drag?

@MoritzHeppler: This has been answered here. Generally, the tip effects have relatively less influence and a weaker vortex strength suffices for the same lift because more air is affected by it. The pressures on the wing are the same, but extend over a smaller chord.

After reading that answer and some others linked there, I'm a bit uncertain about the conclusions I've drawn again. I'm thinking that, if, say, pressure stayed the same along the whole span (without thinking how you'd facilitate such a distribution), the downwash aft of the wing would equal the upwash in front of it. However, this means that no net downwards deflection has occurred, ergo no lift produced. part 1/2

But if the wing is finite, and pressure does move towards ambient as span increases, you would expect the downwash to increase with span too, because it is induced by increased vorticity resulting from the increasing spanwise flow as you move closer to the tip. Could you explain if and where I'm making a mistake in my thinking process? Also I apologise for my difficulty in comprehending the subject, I'm really not sure why I have so much trouble with it. part 2/2

@MoritzHeppler The combination of high vorticity and a small spanwise vorticity gradient near the center produces the same downwash as a low vorticity with a high spanwise vorticity gradient near the tip. Downwash is evenly distributed over span.

In that case I have some reading up to do, because I thought vorticity was solely a byproduct of tip effects, and therefore would increase as you move along span. Again, I'd just like to say thank you for your very detailed answers.

@MoritzHeppler: No, vorticity is highest at the center and decreases towards the tips. Try this answer.

Let us continue this discussion in chat.

Angle of attack AoA, aspect ratio A, and downwash deflection angle E, are linked by:
sin E = 4 sin AoA/(2+A)
Derivation here: Chris Waltham, Flight without Bernoulli https://booksc.org/book/45382205/a4710b

… for small angles, aspect ratios > 5 and lift curve slope $c_{L\alpha}=2\pi$.

downwash downstream of a wing induces a net angle of attack that is lower...

So add in a horizontal stabilizer to your picture and raise and lower your AOA (you can drop flaps too).
What is interesting is that, since the horizontal stabilizer is generally configured to produce negative lift (down force), the down wash will increase its negative AOA.
When dropping flaps in a 172, the nose up pitch is very noticable.

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Why do the A220 cockpit seats have a cutout?
Why do cockpit seats on the A220 have a cutout on the bottom cushion? The answers to Aircraft pilot's seats: what is the notch for? explain that these cutouts allow for easier maneuverability of the yoke. However, this A220 cockpit has no yoke. Why does this cockpit have the cutout?

(source: thepointsguy.com)

Maybe it's to facilitate peeing into a bottle and avoiding the complications of having to go back into the passenger cabin to a lavatory  :)

As we have seen in a previous question, the A220 is a re-branded Bombardier CSeries.
The CSeries started flying in 2013. At the time Bombardier's other commercial jet was the CRJ, that started flying in 1999, 14 years prior.
CRJs do have a yoke:

(wikimedia.org)
If you look closely, you'll notice that the seats look identical, indicating that Bombardier probably decided to cut on costs by simply re-using something they had already (and minimizing the parts they would have to support).
Moreover, this answer mentions the need to have the straps as close to the pilot as possible, and this is achieved with the notch. A redesign of the seats has probably been deemed not worthy of the costs.


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How frequently are avionics on large commercial aircraft updated?
How frequently are avionics on large commercial aircraft updated? And how are the systems updated?

Infrequently. Large fleets, lots of down time, lot of equipment to buy.
The fleets are cycled thru at a refittng center where the panels are disassembled and re-assembled. Here is one example

Though the post doesn't specify it is tagged with software, which wouldn't necessarily require lots of new equipment.

Well, being a hardware engineer, I was looking at from the hardware perspective.  I just had new hardware put in my airplane (solid state gyros, GPS/Nav/Com, Transponder, Engine Monitor). And today the software was updated in the gyros and GPS/Nav/Com, which I never had hardware before that could be updated like that.

Even software doesn't get updated that often (Databases like maps are a different animal) For example, avionics company A might only put out a software update from 6 months to 2 years, depending on the product.


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Why do the jet turbines spin while the engines are turned off?
Why do the jet turbines spin while the engines are turned off? Is this as a result of the wind? Or are the turbines deliberately spun using the APU? If so what is the reason behind this?

I could swear this is a duplicate but I can't find it.

Perhaps a vague resemblance to https://aviation.stackexchange.com/questions/8840/why-was-there-a-rattling-noise-coming-from-the-left-engine-of-a319  That question asks about the rattling noise heard due to the windmilling of turbofans.

They have "turning gear" ; The purpose is to keep the shaft/s turning as the engine cools down to avoid any "sag" . The shafts must be kept perfectly straight.

After shutting down they still have momentum. Or like you said, because of Windmilling - freely turning when the wind impacts the compressor blades.
The APU can, but more often than not doesn't, rotate the engines (overly simplified, not to go into unrelated details).

An aircraft parked in a tailwind can even cause the engines to rotate backwards.                            Can you please expand your comments about the APU? You are implying that the APU is rarely used to rotate the engines when in fact it is used every time when starting the engines.

Yes you are correct of course, but what I meant is that an APU is used for longer periods when powering the aircraft on the ramp - before starting and after shutdown, while when starting the engines it is used only for a few seconds. Emergencies situations during flameouts are another example

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Why do cockpit windows often appear to have a rainbow ‘tint’?
Why do cockpit windows often appear to have a rainbow ‘tint’? It’s similar to what you would see when looking at a shallow puddle of water with oil on top. Here is an example of a B777 cockpit window with the same rainbow effect:


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What would happen if multi engines operated symmetrically?
What would happen if a multi engine operated symmetrically? So if one engine were to rotate counter-clockwise and the other clockwise. What are the advantages and downsides to this?

Not exactly an duplicate, but I believe you can find your answer here.

Related

Are you asking about propeller engines, jet engines, or both?

With symmetrically rotating engines, the P-Factor is, assuming both engines run at the same power, cancelled out. That means the plane will fly straight, instead of yawing to one direction.

@NoahKrasser Looks like the start of an answer if this isn't a dupe.

Oddly, I would consider counter-rotating engines to be asymmetric, but maybe that's just me...

@FreeMan There are several types of geometric symmetry, including rotational, scale, helical, etc. The OP seems to be considering mirror symmetry. What you appear to be considering could be a type of rotational symmetry, if only taking the propellers into account.

I find strange that the A400M case (anticlockwise on engines 2 and 4, clockwise on engines 1 and 3) is not yet mentionned.

A single engine plane yaws to the opposite direction of the engine spinning. This is called the p-factor It's the same with a twin, with both engines rotating into the same direction. Rudder input is needed to fly straight.
When the engines operate symmetrically, this effect cancelles out. The plane is easier to fly.
It's also explained in this video about twins.
An example of a counter-rotating multi-engine plane is the Lockheed P-38 Lightning.

[The P-38] featured two 1,000 hp (746 kW) turbosupercharged 12-cylinder Allison V-1710 engines fitted with counter-rotating propellers to eliminate the effect of engine torque.
Counter-rotation was achieved by the use of "handed" engines, which meant the crankshaft of each engine turned in the opposite direction of its counterpart.

If the engines are turning in the same direction, then if either fails, the net p-factor will not be the same. See: Critical engine.

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How would you design an airplane to counteract a single engine’s left turning tendencies?
How would you design an airplane to counteract a single engine’s left turning tendencies caused by torque, p-factor, spiraling slipstream and gyroscopic precession without pilot input or use of rudder?

Are there detectable forces on the aircraft, such as engine mount strain, which would be proportional to the forces involved?

Make it jet powered and centerline thrust?

How would you design an airplane to counteract a single engine’s left turning tendencies caused by torque, p-factor, spiraling slipstream and gyroscopic precession without pilot input or use of rudder?

Make the airplane asymmetric.  I'd make one wing longer than the other, put more tilt on one wing, put the rudder off center, sweep one back more than the other, or all the above and possibly more.  We expect aircraft to be symmetric but they don't have to be, and there are historical examples of aircraft that are asymmetric. https://en.wikipedia.org/wiki/Asymmetrical_aircraft
Why make aircraft symmetric?  Because it's easier to design it that way, I guess.  Another is because if engine power is lost a symmetric glider would be easier to control than an asymmetric one.
My guess is that there's a little truth to all the reasons I thought up on keeping the airplane symmetric.  A big reason to keep the airplane symmetric, at least by my estimation, is that the off center thrust of a single propeller is going to be so small in most cases that it's not a real concern.  If an airplane is built to be asymmetric then the direction of rotation on the propeller is fixed, putting in a different engine will throw off the design. Just how much turning torque will have to be designed into the asymmetry may be difficult to know while designing the airplane, then if you get it backwards (because the engine turns the opposite direction from what was expected) there's going to be big problems for someone.
The most common method to counteract the single engine torque is to use counter rotating propellers.  This can be with coaxial propellers on the center line or symmetric pairs off center.  A single engine does not mean it must have a single propeller.  The Wright brothers used a single engine to drive two propellers by belts, one belt had a twist in the path to the propeller to reverse the rotation.  This solution is as old as the airplane.
I will say that the answer offered by @Zeus, some kind of autopilot to manage the turning moment of the propeller, is perhaps better than the two I offered above.  Designing asymmetry into the aircraft is going to be difficult to get right.  Counter rotating propellers is complicated.  An autopilot is going to be complicated too, but perhaps far less complicated than any other option.

Look at the designs for literally hundreds of powered free flight model airplanes.  Every one is designed to fly in a stable turn while both climbing under power and gliding after the engine run stops.  And all do this with very subtle-seeming trim adjustments in roll, yaw, and thrust line.  Very common is to adjust the glide by warping or adding small tabs to the flying surfaces (usually giving a large circular glide path), then adjust powered flight by adding down and right thrust (to counteract the left turning and climbing tendencies from torque, P-factor, and increased flying speed).
Very little adjustment is likely to be needed to a light plane anyway -- pilots habitually trim aileron, rudder, and elevator for "hands-off" stability, with the result that there are a large number of accidents that have occurred where a running airplane (due to engine being warmed or hand started by a single pilot) has gotten unchocked and taken off by itself, sometimes flying without crew for half an hour or more (I think the record was one in Australia that circled near the airport for four hours, until running out of fuel).  The biggest consideration is that it may be necessary to set up at partial throttle, or the airplane will tend to climb to its service ceiling.

This can easily be done by mounting the engine at a very slight yaw angle to the fuselage, of order ~ 1 or 2 degrees, in the direction opposite to the turn. This tips the thrust line off-axis and helps counter the turning tendency.

Single engines on model aircraft are typically mounted yawed and pitched downwards a bit.

Single Engine Twin Prop or Contra-rotating Propellers.
It isn't the engine that causes the turning, it's the propeller. In the twin prop case I'd specifically make the two props rotate in opposite directions.
Of course such a design has other major disadvantages, but it would achieve your desired objective.

Or contra-rotating props? https://en.wikipedia.org/wiki/Contra-rotating_propellers

Thank you. I meant to include contra-rotating props as a subset of twin props.

Well, if rudder deflection is required to counter yaw when full power is applied, it stands to reason you could simply angle the vertical stabilizer by a corresponding amount.
However, the logical follow-on question would then be: "how would you design an airplane to counteract this new airplane's right turning tendencies at less than full power?"
There are tradeoffs to be made in all designs, and a moveable control surface is simply the easiest and best solution to this momentary "problem".  (Let pilots be pilots!)

But power is not at constant all the time, is it?  Is the v.stab angle that's correct for WOT also correct for idle?

@Harper-ReinstateMonica, that’s precisely my point!  Meaning that the pilot needs a moveable control surface to counter the effect.

Disclaimer: This answer borrows liberally from this one, but since it could not be found when the question was asked, I add parts of it here.
The direction of rotation of the propeller introduces an asymmetry which designers try to mitigate by adding more asymmetries. Specifically, a right-turning tractor propeller (clockwise from the pilot's viewpoint) will swirl the propeller wake in the same direction which adds a negative sideslip angle on the vertical tail (which sticks up into the upper half of the wake only). By pointing the axis of rotation of the propeller slightly to the right (right sidethrust), this sideslip angle can be reduced.
When MBB tried to rebuild an old Me-109, they initially replaced the missing vertical with a symmetrical one, including a symmetrical airfoil. Years later, original drawings surfaced (in Spain, IIRC) which showed that the original vertical had camber. When the new vertical was replaced with the original design, flight characteristics improved markedly.
The propeller axis can also point slightly down in order to move the thrust line closer to the center of gravity, reducing thrust-related trim changes, and to reduce the P-factor effect (sideways shift of the thrust vector) at high angle of attack. This is called downthrust. One example would be the RR Griffon-engined version of the Supermarine Spitfire: When the new engine was installed, its lower thrust line required 2° more downthrust.
This is one of the few topics where the English version of Wikipedia stays schtum; only the German version has an article on it (Motorzug and Motorsturz).

You are putting forth an impossible task.  For example, as an aircraft begins to accelerate, then rotates to take off, different factors are in play in different amounts at different times, as the "angle-of-attack" of the fuselage (relative to the airflow) changes, and the motor rpm changes, etc.
In at least one case, engine-related turning tendencies were countered by making one wing (or one set of wings if it was a biplane) longer than the other.

Of all tricks, this hasn't been mentioned yet (and is not excluded by the question):
Autopilot
Or more specifically, any sort of artificial control/stability augmentation system.
On many airplanes, there is a dedicated part of it specifically for the stated problem. Usually it is called Yaw damper, although this term is somewhat misleading: damper is only meant to dampen yaw oscillations. Yet in practice, the same subsystem (with the same switch) often also provides the autorudder functionality, negating sideslip.
Of course, it is useful not only for single engine airplanes: it works for any asymmetry, including a turn.

The question says "without pilot input or use of rudder", so I guess this is excluded.


text:
What are all the different ways pilots can navigate?
What are all the different ways pilots can navigate? What are they in simple terms and their unique advantages/disadvantages?
EX:

Dead-reckoning?
VOR?
GPS?
ATC Directives?
Others?

This is a broad question, but here goes...
Visual Navigation
Pilotage, otherwise known as IFR (I Follow Roads). The pilot looks out the window and navigates using reference to the ground by observing landmarks (cities, roads, bodies of water, charted structures, etc). This can be done using any kind of map but an aviation sectional is recommended because it includes useful information such as the Maximum Elevation Figure for a given quadrant, as well as prominently-displayed airports and associated information.
Dead reckoning. The pilot plans a route to a destination (either direct or via waypoints) and calculates the proper heading to fly using a flight computer. This heading will take into account discrepancies between magnetic north and true north, winds aloft, etc. Because the winds and aircraft performance may change, the pilot will have to occasionally use pilotage to reconcile their planned route with their actual ground track.

Instrument Navigation
There are various ground-based radio navigation aids. One of the very early methods was the "A-N" system where two radio transmitters continually broadcast either a Morse "A" (.-) or "N" (-.). If the pilot heard only a single tone, it meant they were directly between the transmitters and therefore on course; otherwise they would hear one letter stronger than the other. This system is not used anymore.
Then there are Non-Directional Beacons. An instrument in the airplane can listen for the radio signal and can point a needle directly TO the beacon but cannot provide any more information than that. A small number of NDBs still exist but they are not really used either.
A VHF Omnidirectional Range instrument can point to the VOR beacon and can display precisely which radial of the beacon the aircraft is on. If both are equipped with Distance Measuring Equipment, the instrument will also show the slant-range distance (i.e. length-of-hypoteneuse) to the beacon, which allows the pilot to precisely locate themselves in space.
An Instrument Landing System is two antennas, one providing lateral guidance to a runway and the other providing vertical guidance. The instrument in the aircraft indicates whether the the pilot is aligned with each radio signal or is off-course (and by how much).
Using VOR receivers, an aircraft can fly along defined airways in the sky.
If the aircraft is equipped with a suitable system, the pilot can navigate directly to a given waypoint. This is known as Area Navigation (RNAV).
The system may be an Inertial Reference System which is primed at startup with its initial location and then uses gyroscopes to track minute changes in the aircraft's acceleration, allowing it to determine its position throughout the flight. It could also be a Flight Management System which uses VOR-DME information to automatically navigate directly as opposed to along pre-defined airways. Or it could use the Global Positioning System (or other satellite constellation like GLONASS) to find its position over the Earth.
Depending on the aircraft, the FMS may provide guidance to the pilot about where to position the control surfaces to align with the planned route, or it may simply display the route relative to the aircraft on a "moving map" akin to a smartphone's map display and allow the pilot to correct course as they see fit.

ATC Guidance
When in radar coverage, ATC can provide navigation services for the pilot by issuing headings—called vectors—for the pilot to fly. The pilot does not have to do any navigational work at all, but must trust ATC to guide them properly to their destination.
At some airports, where equipment and training allow, ATC may even be able to issue vectors all the way down final in lieu of the pilot navigating on a ground-based or RNAV approach procedure.

Also PBN, RNP, LPV

@mins: IIRC, RNP is a flavor of PBN, and both are just standards for how accurate your RNAV system has to be—they are not navigation systems in and of themselves. LPV uses an RNAV system with what are essentially ground-based GPS units to provide enhanced vertical precision but it is still a flavor of RNAV.

I'd say LPV, RNP and RNAV are flavors of PBN.

Pressure pattern navigation, doppler radar navigation?


text:
Are ILS approaches taught as part of instrument rating?
Are ILS approaches taught as part of instrument rating? What categories specifically?

CAT I?
CAT II?
CAT III A?
CAT III B?
CAT III C?

Are you asking about a specific country, or just in general?

Others have covered what is taught for the instrument rating, but it's important to note that having an instrument rating is actually a prerequisite when applying for ILS CAT II authorization, so higher level CAT ratings are covered by separate training and licensing - you work your way up.

In the US, almost all instrument students learn how to fly an ILS CAT I because that's what's installed in most aircraft. You could get an instrument rating  by using an LPV approach instead, though. The FAA's Instrument Rating Airman Certification Standards say (emphasis mine):

Localizer Performance with Vertical Guidance (LPV Minimums)
Localizer performance with vertical guidance (LPV) minimums with a
decision altitude (DA) greater than 300 feet height above touchdown
(HAT) may be used as a nonprecision approach; however, due to the
precision of its glidepath and localizer-like lateral navigation
characteristics, an LPV minimums approach can be used to demonstrate
precision approach proficiency if the DA is equal to or less than 300
feet HAT.

In my flying club, we have a Piper Cherokee without a functioning glideslope indicator in the panel. It's still fine to fly it under IFR using GPS (RNAV) only because the GPS display can provide lateral and vertical guidance. In theory, a club member could get their instrument rating in that aircraft without ever flying an ILS.
(But even in that case, LPV is designed to act like ILS anyway, so the pilot's skills would transfer well to an actual ILS approach.)

Garmin now makes an IFR GPS/COM unit with no NAV (VOR/ILS) functionality, so maybe there’s a market, but I wouldn’t recommend it for a trainer.

What exactly your training (and checkride) includes will be dictated by what the plane you’re using is equipped for. These days, that typically means ILS/LOC (Cat I only), VOR/DME and RNAV.
Some students might get a few ASR or PAR approaches if they are near a military base that offers them. If you’re training in a very old plane, you might also do NDB approaches, but most ADFs have been removed (or at least deactivated) by now specifically to avoid that nightmare.
In theory you could get an authorization to do ILS above Cat I, but few trainers are suitably equipped, and few airports are either for that matter—and the ones that do are typically major airline hubs unlikely to welcome training flights.

Yes, for my Pat 61, FAA issued, Private Pilots License based, Instrument Rating, ILS's were a routine part of the training, we only flew CAT I since we were flying a Piper Archer and not equipped for anything beyond that. There is a good overview of the differences here.
To fly a CAT II approach in a category A aircraft you would potentially need special authorization as noted in FAR 91.139 but that also specifies

Such authorization does not permit operation of the aircraft carrying persons or property for compensation or hire.

And recent rulings by the FAA may consider flight training "for hire" so it might not be legal either way.

In Europe approaches below CAT I are considered as "low visibility operations" (LVO). Each operator (airline) has to apply for the authorization to perform LVO from their CAA. They need to have LVO procedures described in the manual, provide training for the pilots and have capable aircraft in their fleet.
For the pilots the rating to fly LVO is tied to the operating procedures of each airline so even if you have instrument rating you have to prove yourself to every operator you intend to fly LVO with. Rating is valid for six months.


text:
What is "(CFMCC)" on an ILS approach chart?
I'm studying the ILS or LOC RWY 3 approach chart for KMKC. I'm trying to figure out what "(CMFCC)" at the runway means.

Is it a computer navigation aid?

A point shown in parentheses like this is called a Computer Navigation Fix (CNF). If it didn't fall right at the end of the runway, it would be marked with a small X. It's defined in the legend on page 39 (page 41 of the PDF) of the Terminal Procedure Publication User's Guide.
These points are only used to define the navigation track in the flight computer. They should not be used by ATC, but pilots could use them for reference if their FMC or GPS shows them. There is a short AOPA article about them, arguing they should be removed from the charts. Here is a much longer PDF that has a bit more detail on their purpose and a lot more detail about making sure their usage and distinction are clear.


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Airfoil- concave top and bottom
I remember building a radio controlled model in the early 90s with concave wing  ribs/surfaces top and bottom...both sides of the wing were undercambered...
It was a very great flying model...60" wingspan...and it flew as well as any other airfoil design...it was a testy build, covering the wing surfaces with monokote..other than that it was a fun craft...never understood how it flew so well by violating all the 'rules?'

Hi and welcome to [aviation.se]! This place is a bit different than most online fora - We're all about questions and answers, not general discussion. Please take the [tour] and read through the [help] to find out what makes a good question - that'll help you get a good feel for the place. That said, I'm not really sure you have an actual question, so this will probably end up getting closed. If you do have a question, feel free to [edit] your post to ask it more explicitly. You can do that even if your post is closed, then it will likely get reopened.

Undercambered bottom follows the "rules", undercambered top has been tried in small scale Kline-Fogleman wing designs. What you are describing resembles a KFm-5b.  A picture or drawing would help.

It's because the "rules" people are traditionally taught about creation of lift, basically that a wing is a semi-venturi that is sucked up by venturi effect as it moves, is a gross oversimplification that overlooks most of what is going on, which is the wing motivating a large package of air to move down and creating a Newtonian action/reaction, of which the venturi effect is a part.
Anything that is more or less flat-ish, moved through the air at some angle, will make some amount of lift if it's able to induce some of the air to move from up here to down there as it passes.  The front door of your house, your hand stuck out the window of a car, or a wing with a weird reverse curve on top.  Enough to make an RC airplane fly at least.  Probably wouldn't work so well with a full size one.


text:
Do carrier-borne aircraft pilots count the seconds on the downwind leg of the carrier?
On carrier landing, someone tells me that the pilots need to count several seconds on abeam leg of the landing pattern, in order to land precisely on the flight deck. Is that true? What do we call for this operation?

Can you please add some supplemental data to your question such as a link to something indicating that this is a thing?  I would think just by intuition that a pilot landing on an aircraft carrier could not use time as a measure of when to turn due to variables such as speed of the landing pad(ship), speed of the water itself, and wind.  For example, you could be confusing this with instrument procedures that would instruct a pilot to fly for 1 or two minutes from a fix, the fix being the carrier in this case.

Thank you very much! Maybe I misunderstood the question.

Standard practice is to turn abeam. This results in 10-15 seconds “in the groove” once you roll wings level on final. Because of the angled deck, the turn to final is more than 180 degrees.
This does vary based on wind. Once, when both the natural winds were high and the ship was in a hurry to get somewhere (luckily into the wind) we saw 50 kts wind over the deck. Turned before the bow, so at the 90 it looked like we were pointing at the round down. Just requires using Mark I mod 0 eyeball to judge off norm conditions

Thanks a lot! It is very helpful!

The target goove length is generally 15-18 seconds.  At least that is what was burned into my memory in the 1990s...


text:
How to correct dynamic stability of UAV fuselages?
I was trying to design a fuselage model of UAV with considering lift coefficient (CL), after this I analyzed stability of both wing on fuselage. First I did the individual analysis for wing and fuselage in which the result of main wing analysis is quite good but after adding fuselage the dynamic stability of the UAV was not perfect.
If any information might be lacking I would love to add details and I am onto sure if my question is reliable for this forum ,if so it would be great if you could suggest a specified forums where I can discuss with this issue.
Thanks in advance.

Which stability derivative are you seeking correction?

Overal dynamic stability in turning and banking.

I don't understand. Dynamic stability (rigid-body) refers to phugoid, SP, dutch-roll, etc., which are affected by their respective stability derivatives, and drag (only for phugoid). Turning and banking aren't typically associated with dynamic stability since they are maneuvers.

I got that point that’s why I was so confused about the factors that affect the dynamic stability of fixed wing plane and I will try to reconsider whole analysis with your point of view. If you are comfortable It would be great to talk to you in details.

You need to present some data here in order for people to help you. What are you analyzing exactly? What are you comparing, and against what? What exactly is inconsistent, and against what? As the OP stands, I don't even know what your issues are.

If it would help, consider turning and banking as unstable conditions.  You want your plane stable on 3 axes with no control input, but unstable when a control input is added.  Otherwise, you cannot pitch, yaw, or roll.

Thank you so much Mr.DiGiovanni. I got my answer.


text:
What is this single-engine low-wing propeller plane?
I found this picture in an article about constant speed propellers, but there was no reference to the type of aircraft. The Flickr account that first posted the image doesn't exist anymore. I did some research myself, I thought it could be a Cessna or a Beechcraft, but I don't know much about it and none of the models I found was a perfect match.

That’s a Piper PA-28R Arrow.  Most likely an PA-28R-201 Arrow III, by the looks of it.

It looks exactly like the Arrow III that I sometimes fly, except this one has cowl latches and a tail beacon.

Are there any specific features that are characteristic of that particular model?

Chiefly the Arrow III has the tapered wing as opposed to the Hershey bar wings of the older Arrow I/II aircraft.  The III also holds 72gal usable fuel as opposed to the 48gal useable of the Arrow I/II.


text:
Two Plastic ATP Certs?
I recently got typed in the CL-65 and received my restricted ATP certification. I can’t figure out why but apparently due to the amount of limitations such as PIC in accordance with 61.167 and vmc circle only and Cl-65 vmc circle only lines, they added the rest onto a second plastic certificate. I have a 1 of 2 and a 2 of 2 card. Has anyone seen or heard of this happening to them or anyone else?

I've seen one pilot with so many additional ratings and limitations they had three plastic cards.


text:
What ISA temperature to use in the density altitude calculation?
In the density altitude formula: DA = PA + [120 x (OAT - ISA Temp.)], should one use the ISA temperature at the field elevation or the ISA temperature at the pressure altitude?

Calculating Density Altitude
Density altitude in feet = pressure altitude in feet + (120 x (OAT - ISA temperature))
Altimeter Pressure altitude is determined by setting the altimeter to 29.92 and reading the altitude indicated on the altimeter.
OAT stands for outside air temperature (in degrees Celsius).
ISA stands for standard temperature (in degrees Celsius).
Keep in mind the standard temperature is 15 degrees C but only at sea level. It decreases about 2 degrees C (or 3.5 degrees F) per 1,000 feet of altitude above sea level. The standard temperature at 7,000 feet msl, therefore, is only 1 degree C (or 34 degrees F).
For example, the density altitude at an airport 7000 feet above sea level, with a temperature of 18 degrees Celsius and a pressure altitude of 7000 (assuming standard pressure) would be calculated as follows.
18 – 1 = 17
17 x 120 = 2040
2040 + 7000 = 9040 feet Density Altitude
This means the aircraft will perform as if it were at 9,040 feet

ISA is 15 degrees C at sea level. For the calculation, decrease temperature by 2 degrees C for every 1,000 ft of altitude above sea level.

This is still ambiguous.  "Altitude above sea level"....of the field or of the pressure altitude?  That's what the asker seems to be looking for.

Look at the sentence previous to that and it should become clear.


text:
Explained intuitively, why does aspect ratio affect induced drag?
Over the last few hours, I've been trying to intuitively understand induced drag, and how aspect ratio affects it. I already know the equations, but while they explain the relationship, they do not really explain anything, I want to understand what is happening physically. I've read on many answers in this community, specially by Peter Kämpf, but I've been unable to attain an intuitive understanding.
I will explain my line of thinking, hopefully I can be corrected on any misconceptions, or wrong assumptions.
First of all, my way of thinking about lift is simply airflow being redirected. If airflow is redirected by a surface, a force in the opposite direction is applied on said surface. This means that for lift to be generated, downwash must exist, therefore induced drag is an inseparable side-effect of generating lift.

Let's imagine 2 theoretical wings, both of which have the same area, but differ in aspect ratio.
If induced drag depends on the downwash angle, why would a longer wingspan reduce the angle? If the downwash angle is reduced, then the amount of air being redirected (total mass) must increase to keep lift equal, how can that happen when the wing area is equal?
All of the sources I am able to find blame induced drag solely on wingtip vortexes, since they cause downwash, but the entire wing is creating downwash, so what gives?
If tip vortexes are what cause induced drag, how does a longer wingspan reduce the induced drag coefficient? As an example: If the span of rectangular a wing is increased without changing the chord length, the aspect ratio will increase, which according to the math, will lower the induced drag coefficient. How does a longer wingspan affect the vortexes such as to reduce the downwash?

"Intuitively", airplanes wouldn't fly at all. So it's difficult to understand what variety of "intuitively" would be a satisfactory answer here.

@PeterDuniho, well, that depends on your experience and powers of observation I guess, but I disagree with that statement.  If you have ever observed and felt a fan blowing air, ever stuck your hand out of a car window to play with the AOA of your palm, it isn't that big a leap in imagination to link the idea of a propeller and a wing, and to thereby grasp the fundamental forces that allow a heavier than air craft to fly.

I have a hypothesis which is that our intuition about flow comes from observations of water. In that case, if you observe water rushing down a river and meeting rocks and other obstacles, you will come the wrong conclusion. If you don't like that, let’s just go with the fact that if you intuitively assume air is inviscid, what the great Euler did, then you also get no lift. So, we might be able to observe the effects of the wind from a storm, but that does not give us an appreciation for Navier-Stokes. Hence, @PeterDuniho is making a reasonable statement.

Let's imagine 2 theoretical wings, both of which have the same area, but differ in aspect ratio.

Then the wing with the higher aspect ratio also has more span. This is what counts.

If induced drag depends on the downwash angle, why would a longer wingspan reduce the angle?

Because the wider wing will affect more air. Think of the air affected by the wing as what flows through a tube, the diameter of which equals wing span. Like in the picture below.

Of course, for clarity, the amount of bending the stream tube undergoes due to the wing is greatly exaggerated here. In reality it is a few degrees at most.

how can that happen when the wing area is equal?

Wing chord does not count here as long as the amount of stream tube bending can be done by the skinnier wing. More chord will not affect the result. Only when too much is being asked of a limited chord will the wing stall. At lower lift coefficients, more chord will only increase friction drag.
In reality the influence of the wing fades the more you move away from it. This picture of a stream tube is a simplification which you will also find in propeller theory, and it gives the correct result, because what you neglect in the far field you compensate by assuming a constant influence over the near field.

All of the sources I am able to find blame induced drag solely on wingtip vortexes

You do well to disregard those sources. They have the causality backwards.

This was a great answer, as always, and it fundamentally improved my understanding of lift as well as gave me a very simple (and intuitive!) way to explain to others why wingspan matters so much for efficiency. However I honestly struggle to understand the graphic. I know what it wants to show, but I just can't get my eyes to see what they're supposed to there. I know I should be seeing a tube deflected downward, but I see two circles, one tangent to a wingtip and the other floating in space. Just an FYI on an otherwise impeccable post.

@KennSebesta Thank you, that is the kind of feedback which is most helpful for me. I will try to improve the graphic.

@KennSebesta Is this any better? Like last time, I used Sketchup and increased the contrast, but I'm afraid it is not fundamentally different.

Yes, I think so! The shading helps tons.

@PeterKämpf "affect more air" means more air in kg/s?

@user628075 Yes, exactly. A larger mass per unit of time.

@user628075 Yes, exactly. Which explains the much better efficiency of turbofans vs. turbojets. Large, slow propellers have the highest subsonic efficiency.

Do not focus on aspect ratio.  Also, do not focus on drag coefficients.  Instead, work in terms of dimensional drag and lift. Airplanes don't fly on coefficients, they fly on forces...
Starting from a simple parabolic polar.
$C_D=C_{D,0}+\frac{C_L^2}{\pi\,e\,AR}$
$D=C_D\,q\,S$
$L=C_L\,q\,S$
$AR=\frac{b^2}{S}$
Throwing all this at dimensional drag step by step...
$D=C_{D,0}\,q\,S + \frac{C_L^2}{\pi\,e\,AR}\,q\,S$
$D=C_{D,0}\,q\,S + \frac{\frac{L}{q\,S}^2}{\pi\,e\,AR}\,q\,S$
$D=C_{D,0}\,q\,S + \frac{L^2}{\pi\,e\,AR\,q^2\,S^2}\,q\,S$
$D=C_{D,0}\,q\,S + \frac{L^2}{\pi\,e\,AR\,q\,S}$
$D=C_{D,0}\,q\,S + \frac{L^2}{\pi\,e\,\frac{b^2}{S}\,q\,S}$
$D=C_{D,0}\,q\,S + \frac{L^2}{\pi\,e\,b^2\,q}$
The first term is the dimensional parasite drag.  The second term is the dimensional induced drag.
Notice the appearance of the term $\frac{L}{b}$.  We call this the span loading.  Instead of aspect ratio, the span loading is what is important for induced drag.  Or, for fixed lift, the span is what is important.
The area (and aspect ratio) becomes important when you want to figure out what speed your best L/D occurs at -- and other things -- so it isn't totally unimportant.  However, the thing to recognize from this analysis is that induced drag is reduced by increasing span.
Spreading the act of generating lift over a greater span will reduce induced drag.  It isn't about some ratio of wing shape -- it is about spreading the lift across a wider span.  Similarly, the shape of the lift distribution is a driver of induced drag -- you already know elliptical is best.
Something similar happens for induced power for rotorcraft.  Because of this, all aircraft (that want to be efficient) want as large of a span (diameter) as they can get.  Consequently, with very few exceptions, all aircraft are span constrained.  Some new aircraft designers believe that they don't have a span constraint -- they just haven't figured out what their span constraint is yet.  A great early step in design is to figure out your span constraint if your customer didn't state one.

Your understanding of induced drag is correct. It is caused by turning the air flow and the force that does it must be tilted, otherwise conservation of energy would be violated.
The stream ‘tube’ affected by the wing is obviously as wide as the wing, and always considered to be roughly as high as wide. That is, wings with higher span affect air to greater height above and below them and therefore much more of it. This matches the fact that, for given lift, induced drag is inversely proportional to the square of span.
An intuitive, approximate, explanation is that the air below the middle can't escape directly to the sides and must go further down the wider the high-pressure region is, and similarly above the wing the air from sides is already used up for filling above the wing tips, so air from higher up is needed to fill in in the middle.
Or in other words, the affected region is approximately circular, because the pressure is being equalized in all directions.
The lower aspect ratio wing has to fly at higher angle of attack to compensate. I think, but am not completely sure, that it can do that because the longer chord allows turning the air more gradually—with the same lift and the same area, the pressure drop is the same (pressure being force per area), but it acts longer on the stream—so it can be turned by higher total angle before the flow separates. But it is to an extent only—both ${C_L}_{max}$ and ${C_L}_\alpha$ depend on the chord length and the lower aspect ratio wing will produce less lift.

This is my interpretation.  See if it helps.  Induced drag can be thought of as the energy consumed in making lift, in other words, the energy consumed in inducing a package of air to move down as a result of the wing's passage.  It's the energy consumed in accelerating a mass; wing, propeller, helicopter rotor, it's all the same.
Vortices are just a manifestation of energy "leakage" in the process of inducing a package of air to move down.  Some of the air, instead of being induced to move down, escapes around the wing tip, and it extends well beyond the core right at the tip were the strong vortice is; there's a large flow field circulating around. It's like a snow plow where snow near the ends of the plow is able to escape around the ends and avoids being pushed forward.
A higher aspect ratio wing is moving a longer and skinnier package of air compared to a low aspect ratio one of the same area that is moving the same total mass of air.  This means that the escape route around the tip is a smaller proportion of the total mass affected, so the overall losses, the amount of leakage, is a smaller part of the overall package of air being induced to move down.
If both the high aspect wing and low aspect wing have the same area, meaning they are both attempting to redirect more or less the same total mass of air, the high aspect one with the lower losses from tip leakage*, relative to the total package of air affected,* is able to get more work from the same package of air.  If it's getting more work out of the same package of air, it can operate at a slightly lower angle of attack for the same net lift force generated, and needs less total energy to generate that lift force, and therefore has less induced drag.

I am pretty sure the tip leakage is a red herring. The wing with larger span is affecting a lot more air.

But the chord is narrower. The air package is longer, but shallower.  In any case, then why to end plates work (if large enough) if not to inhibit the circulation?

The end plates force air higher above and lower below the wing to be affected and contribute to the lift creation. So you are kind of correct, they prevent circulation as in the air below being pushed to the sides rather than down and the air from the sides instead from above filling in, but note that the scale is again comparable to the wing span and the “large enough” means much higher than the wing span here.

Starting with the simplest example, a fully symmetrical airfoil, aspect ratio (of a straight wing) can be described as the ratio of area to chord, or area to span, or ...

higher ratio of leading edge to area

Why is this important?
Because the total lift vector here is pointing forwards, creating a thrust component!
Yes, that's right, induced thrust!

lowers the overall induced drag of the wing.

That, and proportionally lower interferences at the wing tip and fuselage make high aspect wings more efficient for gliding.
It's important that Reynolds Number also plays an important role here.
For very slow soaring birds, such as vultures and eagles, the low aspect wing is actually better to catch the energy of updrafts.  In much the same way as a circular parachute is better than a long thin one, this type of wing cannot take advantage of very low net drag contribution of upper forward wing lift because it is too slow (Reynolds number too low to generate it) and there is greater pressure "leakage" from the bottom due to the higher perimeter to area ratio of the higher aspect design.
But in size and speed from the albatross to full scale gliders, high aspect ratio is the way to go for best glide distance.
This leads to the conclusion that "top lift" mechanism (Coanda/Bernoulli) generates less induced drag than simple Newtonian action/reaction deflection of air from the bottom of the wing for a given amount of lift.

Can you please better explain the "induced thrust" phenomenon? Maybe with a practical example. And why Bernoulli generates less induced drag than Newton? Thanks

@sophit the forward upper surface of the wing has its lift vector tilting ahead.  This decomposes into vertical lift and a bit of forward "thrust".  Go to Airfoil Tools on the net and see how Reynolds number affects L/D ratios.

Ok but when does it happen? Do you have a practical example?

When the Reynolds number is high enough.  This is why, 100 years ago, as planes got better engines, wing design changed by filling in the wing bottom (no more undercamber).

Because percentagewise the tips are a much smaller part of the whole lift. So there are less vortices generated at the tips and that means less induced drag.


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Why can't turbojets or turbofans be overtemped or overtorqued the way turboprops can?
Turboprops that aren't FADEC controlled can be overtorqued or overtemped if the power lever is moved too far forward yet I have never heard of a jet that can't be "firewalled", FADEC or not. Why is this?

You certainly can. The equivalent to overtorquing is called overboosting and is defined as an exceedance of the primary thrust setting parameter, N1 or EPR.
Modern FADEC engines contain software protection, but it is certainly possible in mechanically controlled engines. Thus, older aircraft, such as the DC-9 have mechanical or electronic controls which set N1/EPR bugs depending on flight condition and outside temperature.
EGT exceedances are also possible. Many, if not most, modern FADEC turbofans do not have EGT protection in normal operation so pilots do need to keep an eye on the EGT gauges during high power situations, especially when ambient temperatures are high and the engines are worn.


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Landing currency day and night on same ride?
Assume you know when sunset was on a particular day you decided to fly (e.g. 8:30 local time). If you took off at 8pm, repeated 3+ landings in the pattern, then left the pattern for about half an hour, returned into the pattern at home airfield, did 3+ more landings to full stop at night...did you achieve the objective of landing currency for both day and night, and if so how do you normally log the landings?

Welcome to aviation.SE! I'm assuming that you're asking about FAA regulations (please always tell us which country/regulations you're asking about). If so, then since night currency also meets the day currency requirements, why not just do the three night takeoffs and landings?

As pilots we often talk about night flying and daytime flying meaning when it is dark or light, but for logging time and for currency in the US there are specific definitions that we must pay attention to.

FAR 1.1 General Definitions
Night means the time between the end of evening civil twilight and the
  beginning of morning civil twilight, as published by the American Air
  Almanac, converted to local time.

Day is not defined in the FARs but the definition of night implies that it is the time between the beginning of morning civil twilight and the end of evening civil twilight.
The Air Almanac is published annually on CD-ROM but you can find sunset, sunrise, and civil twilight times for specific locations at the US Naval Observatory website or in ForeFlight.
The time between sunrise/sunset and twilight is 26-30 minutes depending on the time of year. Since you can easily find sunrise/sunset information in newspapers, the weather channel, etc. you can estimate twilight fairly easily.
Currency

§61.57 (b) (1) … no person may act as pilot in command of an aircraft
  carrying passengers during the period beginning 1 hour after sunset
  and ending 1 hour before sunrise, unless within the preceding 90 days
  that person has made at least three takeoffs and three landings to a
  full stop during the period beginning 1 hour after sunset and ending 1
  hour before sunrise, and…

VFR Weather Minimums
Only Class G airspace has different minimums depending on night and day and they use the standard night definition—end of evening twilight to the beginning of morning twilight.
Aircraft Lights
Aircraft lighting is required between sunset and sunrise.

§91.209 During the period between sunset and sunrise no person may 1.
  operate an aircraft unless it has lighted position lights, 2. park or
  move an aircraft in an area of an airport where night operations are
  being conducted unless it is clearly illuminated, has position lights,
  or is in an area marked by obstruction lights.

Aeronautical Experience Requirement
In order to obtain a private pilot certificate night training is required. The commercial pilot certificate required solo night flights. In these cases the standard night definition—end of evening twilight to the beginning of morning twilight—applies.
Special VFR
AIM 4-4-6 g. Special VFR operations are prohibited between sunset and sunrise unless the pilot is instrument rated and the aircraft equipped for IFR flight.
Logging Night Flying Time
Logging of night flight should be made in accordance with Part 1 definitions, which is from the end of evening civil twilight to the start of morning civil twilight. This differs from the definition used for night currency.
Summary
• Position lights – sunset to sunrise
• Special VFR – except sunset to sunrise unless instrument rated
• Carry Passengers – 1 hour after sunset to 1 hour before sunrise
• Everything else – evening twilight to morning twilight
The answer to your question.
Now that we have that out of the way, we can look at the requirements for carrying passengers.

§61.57   Recent flight experience: Pilot in command. (a) General
  experience. (1) Except as provided in paragraph (e) of this section,
  no person may act as a pilot in command of an aircraft carrying
  passengers or of an aircraft certificated for more than one pilot
  flight crewmember unless that person has made at least three takeoffs
  and three landings within the preceding 90 days, and—
(i) The person acted as the sole manipulator of the flight controls;
  and
(ii) The required takeoffs and landings were performed in an aircraft
  of the same category, class, and type (if a type rating is required),
  and, if the aircraft to be flown is an airplane with a tailwheel, the
  takeoffs and landings must have been made to a full stop in an
  airplane with a tailwheel.
(2) For the purpose of meeting the requirements of paragraph (a)(1) of
  this section, a person may act as a pilot in command of an aircraft
  under day VFR or day IFR, provided no persons or property are carried
  on board the aircraft, other than those necessary for the conduct of
  the flight.

You can remain current for carrying passengers in the daytime by making three takeofffs and landins either with or without passengers. If you are not current, you may regain currency as long as you don’t have passengers.
A separate regulation governs night currency—where night is 1 hour after sunset until 1 hour before sunrise.

§61.57   Recent flight experience: Pilot in command.** b) Night
  takeoff and landing experience. (1) Except as provided in paragraph
  (e) of this section, no person may act as pilot in command of an
  aircraft carrying passengers during the period beginning 1 hour after
  sunset and ending 1 hour before sunrise, unless within the preceding
  90 days that person has made at least three takeoffs and three
  landings to a full stop during the period beginning 1 hour after
  sunset and ending 1 hour before sunrise, and—

If you are night current then you have satisfied §61.57 (1) and so you are also day current.

Notwithstanding the fact that legal night starts 1 hour after the 8:30 sunset per FAR 61.57(b),

(b) Night takeoff and landing experience. (1) Except as provided in paragraph (e) of this section, no person may act as pilot in command of an aircraft carrying passengers during the period beginning 1 hour after sunset and ending 1 hour before sunrise, unless within the preceding 90 days that person has made at least three takeoffs and three landings to a full stop during the period beginning 1 hour after sunset and ending 1 hour before sunrise, and—

say you split your flying between some landings before 9:30 pm and some after, sufficient to meet the requirement.
It's simple.  The time you were airborne prior to 9:30 goes in the "Day" column, and the time you were airborne after 9:30 goes in the "Night" column.  In "Remarks" you write in something like "3 day landings and 4 night landings completed".
That's all you need to do.

There is landing currency, and there is night landing currency, but I don't think there is "day landing currency." So if you get 3 landings (also 3 takeoffs) at night, everything else is superfluous, yes?

I thought about that, but the FAR linked specifically mentions "day VFR" for day currency, so I'm not sure that just doing the night landings covers everything, although common sense says it should.  They seem to have written it in a way that requires a lawyer to parse the language, as usual lol.

To update currency (i.e. you're still current, just setting a new date), I think 3 at night & you're complete. However, to regain currency without somebody else acting as PIC (i.e. a CFI), I'd agree that your first 3 have to be day, given the (a)(2) language. Or... that language lets the noncurrent left-seater regain currency with a required SIC in the right seat, day only. Agree that it's murky.

@JohnK Night for logging time starts about 1/2 hour after sunset and ends about 1/2 hour before sunrise. CFR §1.1   General definitions.
Night means the time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the Air Almanac, converted to local time.

@JScarry I was going to say that originally until I looked up FAR 61. Why does it say 1 hour?

The reg you mentioned is a requirement to act as pilot in command and not to log PIC or any other time.


text:
Are DME arcs coded in the CIFP data file?
I use a git project (https://github.com/rstory1/parseCifp) to transfer the FAA CIFP formatted file into a database, but noticed that DME arcs don't seem to be carried over. Looking into the FAACIFP18 file, I can't seem to find it either for some sample airports (e.g. KMTN). Any FAACIFP experts who can chime in on where exactly they are published in this cryptic format, if at all?

Are you talking about the KMTN VOR DME 15 approach?  This is the DME approach to a runway.  It is the only procedure I have ever seen like this?  The procedure is also not in an GPS or FMS that I am aware of.


text:
IFR requirement for altimeter question (i.e. +/- 75 feet)
What if the ATIS/AWOS/ASOS results in a very low or very high altimeter setting (i.e. barometric pressure)? Surely this setting will result in an altimeter setting way outside the envelope of the +/- 75 feet related to field elevation? Since each inch of Hg results in 1,000' change...what am I missing w.r.t. the altimeter check?

What do you mean by "very low or very high"? Inaccurate readings? Values below or above the range of the altimeter? Something else?

I'm not sure what you're asking. Setting your altimeter to the correct local setting will make it more accurate, not less accurate. Can you give a specific example with some numbers?

Barometric pressure isn't a constant. Just because you're at sea level, doesn't mean the air pressure is going to be exactly 29.9212 inHg. That's just the average sea-level pressure. So, for instance, if the sea level pressure is currently 30.9 inHg, then all altimeters in the region are going to read 1000 feet below the actual altitude of the airplane.
Those fluctuations are the point of the altimeter corrections provided by AWOS/ASOS/ATIS. By entering the actual sea-level atmospheric pressure into the altimeter, you can correct for those fluctuations and get a more accurate reading of your current altitude.

@wbeard52 Oops, forgot a zero. Fixed!

The barometric pressure given by the ATIS/AWOS/ASOS is what the atmospheric pressure would be at that lateral position at Mean Sea Level. Any elevation above Mean Sea Level would have a lower atmospheric pressure than the same location at Mean Sea Level. Therefore, an atmospheric pressure reading taken on the surface of an airport/airfield with an elevation of 5000 feet would be much lower than the barometric pressure given by the ATIS/AWOS/ASOS of that same field, signifying the 5000 foot difference between the elevation and Mean Sea Level.
Your pressure sensitive altimeter measures the atmospheric pressure, wherever it is, and converts it to feet above the pressure level set in the Kollsman Window. You dial into the Kollsman Window the barometric pressure at Mean Sea Level to determine your altitude above Mean Sea Level.
In the rare case that the barometric pressure is in an extreme abnormal range, the FAA gives restrictions for flight and adjustment tables for barometric pressure in the FAR/AIM. I have personally only seen this happen in extreme weather, like hurricanes. Most people would not be flying in these conditions.

§91.144 Temporary restriction on flight operations during abnormally high barometric pressure conditions.
(a) Special flight restrictions. When any information indicates that barometric pressure on the route of flight currently exceeds or will exceed 31 inches of mercury, no person may operate an aircraft or initiate a flight contrary to the requirements established by the Administrator and published in a Notice to Airmen issued under this section.
(b) Waivers. The administrator is authorized to waive any restriction issued under paragraph (a) of this section to permit emergency supply, transport, or medical services to be delivered to isolated communities, where the operation can be conducted with an acceptable level of safety.

7–2–2 Procedures
The cruising altitude or flight level of aircraft must be maintained by reference to an altimeter which must be set, when operating:
a. Below 18,000 feet MSL.

When the barometric pressure is 31.00 inches Hg. or less. To the current reported altimeter setting of a station along the route and within 100 NM of the aircraft, or if there is no station within this area, the current reported altimeter setting of an appropriate available station. When an aircraft is en route on an instrument flight plan, air traffic controllers will furnish this information to the pilot at least once while the aircraft is in the controllers area of jurisdiction. In the case of an aircraft not equipped with a radio, set to the elevation of the departure airport or use an appropriate altimeter setting available prior to departure.

When the barometric pressure exceeds 31.00 inches Hg. The following procedures will be placed in effect by NOTAM defining the geographic area affected:

(a) For all aircraft. Set 31.00 inches for en route operations below 18,000 feet MSL. Maintain this setting until beyond the affected area or until reaching final approach segment. At the beginning of the final approach segment, the current altimeter setting will be set, if possible. If not possible, 31.00 inches will remain set throughout the approach. Aircraft on departure or missed approach will set 31.00 inches prior to reaching any mandatory/crossing altitude or 1,500 feet AGL, whichever is lower. (Air traffic control will issue actual altimeter settings and advise pilots to set 31.00 inches in their altimeters for en route operations below 18,000 feet MSL in affected areas.)
(b) During preflight, barometric altimeters must be checked for normal operation to the extent possible.
(c) For aircraft with the capability of setting the current altimeter setting and operating into airports with the capability of measuring the current altimeter setting, no additional restrictions apply.
(d) For aircraft operating VFR, there are no additional restrictions, however, extra diligence in flight planning and in operating in these conditions is essential.
(e) Airports unable to accurately measure barometric pressures above 31.00 inches of Hg. will report the barometric pressure as “missing” or “in excess of 31.00 inches of Hg.” Flight operations to and from those airports are restricted to VFR weather conditions.
(f) For aircraft operating IFR and unable to set the current altimeter setting, the following restrictions apply:
(1) To determine the suitability of departure alternate airports, destination airports, and destination alternate airports, increase ceiling requirements by 100 feet and visibility requirements by 1/4 statute mile for each 1/10 of an inch of Hg., or any portion thereof, over 31.00 inches. These adjusted values are then applied in accordance with the requirements of the applicable operating regulations and operations specifications.
Example: Destination altimeter is 31.28 inches, ILS DH 250 feet (200-1/2). When flight planning, add 300-3/4 to the weather requirements which would become 500-11⁄4.
(2) On approach, 31.00 inches will remain set. Decision height (DH) or minimum descent altitude must be deemed to have been reached when the published altitude is displayed on the altimeter.
Note: Although visibility is normally the limiting factor on an approach, pilots should be aware that when reaching DH the aircraft will be higher than indicated. Using the example above the aircraft would be approximately 300 feet higher.
(3) These restrictions do not apply to authorized Category II and III ILS operations nor do they apply to certificate holders using approved QFE altimetry systems.
(g) The FAA Regional Flight Standards Division Manager of the affected area is authorized to approve temporary waivers to permit emergency resupply or emergency medical service operation.
b. At or above 18,000 feet MSL. To 29.92 inches of mercury (standard setting). The lowest usable flight level is determined by the atmospheric pressure in the area of operation as shown in Table 7-2-1.

7–2–4 High Barometric Pressure
a. Cold, dry air masses may produce barometric pressures in excess of 31.00 inches of Mercury, and many altimeters do not have an accurate means of being adjusted for settings of these levels. When the altimeter cannot be set to the higher pressure setting, the aircraft actual altitude will be higher than the altimeter indicates.
Reference: AIM, Altimeter Errors, ¶7-2-3
b. When the barometric pressure exceeds 31.00 inches, air traffic controllers will issue the actual altimeter setting, and:

En Route/Arrivals. Advise pilots to remain set on 31.00 inches until reaching the final approach segment.

Departures. Advise pilots to set 31.00 inches prior to reaching any mandatory/crossing altitude or 1,500 feet, whichever is lower.

c. The altimeter error caused by the high pressure will be in the opposite direction to the error caused by the cold temperature.

7–2–5 Low Barometric Pressure
When abnormally low barometric pressure conditions occur (below 28.00), flight operations by aircraft unable to set the actual altimeter setting are not recommended.
Note: The true altitude of the aircraft is lower than the indicated altitude if the pilot is unable to set the actual altimeter setting.

IFR approved airplanes require a sensitive altimeter and not just a plain altimeter. When you look at FAA FAR 91.205 you will see a distinction between altimeter for DAY VFR and a sensitive altimeter for IFR.
A sensitive altimeter has a Kollsman window and you can adjust the altitude for the current altimeter setting. Once the altimeter setting is set in, the altimeter must read with ±75 of the current location on the airfield.
You would also be required to adjust the altimeter setting anytime you receive a new weather report from ATC or every 100 NM or so in the absence of such a report.
In areas of really high altimeter settings above 31.00" HG, you should set 31.00" HG even if you altimeter setting can go higher.  Other aircraft may not be able to set the higher altimeter setting.
In areas of really low altimeter settings, it is not recommended to operate an aircraft if you cannot set the correct altimeter setting as you will be lower than indicated on the altimeter.  See AIM 7-2-2.